Two methods used to synthesize high‐purity ferroelectric titanate powders in controlled, narrow size distributions, with average particle diameters <1000 A, were: (1) isothermal pyrolysis of barium titanyl oxalate or mixed calcium‐barium titanyl oxalates as low as 550° and 825°C, respectively, average particle sizes depending strongly on the pyrolysis temperature; and (2) hydrolysis of titanate esters in barium hydroxide. Using solvent media of controlled polarity, high‐purity stoichiometric BaTiO3 was obtained with average sizes as small as 100 A. Factors affecting stoichiometry and particle size are discussed in terms of assumed reaction mechanisms.

SynopsisThe solid-state polymerization by y-radiation and postpolymerization of bulk samples of trioxane has been investigated. Different thermal treatment results in radically different initial morphologies of the melt-crystallized trioxane which in turn have a profound influence on the yield and morphology of the resulting poly(oxymethy1ene) (POM). The polymerization yield increases in the following series: melt-crystallized trioxane with an "opaque" (small grains) morphology, as-grown needles, trioxane with a "quasi-transparent" morphology, and finally thermally oriented crystals. Furthermore, little additional POM is formed during repeated polymerization cycles. The observation of an extensive nodulation of the polymer fibrils when the yield is high is consistent with a multiple-stage growth model for the solid-state polymerization of trioxane.

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